The present invention relates to an internal combustion engine system with heat recovery comprising an internal combustion engine with a waste heat passage, an electric motor, a heat recovery assembly comprising a working fluid circulation circuit with a working fluid, a first heat source which is adapted to be heated by the waste heat passage and adapted to heat the working fluid, and an expander engine, which is operated by the heated working fluid, and a splitting device, which is connected to the electric motor and is adapted to be connected to a drivetrain of a vehicle and which splitting device is further connected to the expander engine, so that the expander engine is enabled to drive the drivetrain and/or the electric motor.
In the following, the term “ICE operation modes” is used as abbreviation of “internal combustion engine (ICE) operation modes”. “High load ICE operation modes” are defined as ICE operation modes, where the driving situation requires a lot of driving force, e.g. running uphill or accelerating. “Normal load ICE operation modes” are defined as ICE operation modes, where the vehicle is neither substantially accelerating nor substantially decelerating, e.g. the vehicle is running at constant speed on a high way. “Low load ICE operation modes” are defined as ICE operation modes, where the vehicle requires little driving force, e.g. when the vehicle is running downhill, decelerates or is in motoring or idle engine operation modes (see below). “No load ICE operation modes” are defined as ICE operation modes, where the internal combustion engine is stopped.
The above mentioned idle engine operation mode describes all engine operation states where the engine is running at idle speed. Idle speed is the rotational speed the engine runs on when the engine is decoupled from the drivetrain and the accelerator of the internal combustion engine is released. Usually the rotational speed is measured in revolutions per minute or rpm of the crankshaft of the engine. At idle speed, the engine generates enough power to run reasonable smoothly and to operate accessory equipment (water pump alternator, and other accessories such as a power steering) but usually not enough to perform useful work such as moving the vehicle. For vehicles such as trucks or cars, idle speed is customarily between 600 rpm and 1000 rpm. Even if the accelerator is released, a certain amount of fuel is injected into the internal combustion engine in order to keep the engine running. If the engine is operating a large number of accessories, par-ticularly air conditioning, the idle speed must be raised to ensure that the engine generates enough power to run smoothly and operate the accessories. Therefore, most engines have an automatic adjustment feature in the carburetor of the fuel injection system that raises the idle speed when more power is required.
The above mentioned motoring engine operation mode is defined as the mode, where the engine is running above a certain rotational speed (rpm) but no fuel is injected into the engine. One example of a motoring engine operation mode is when the engine is dragging, i.e. the vehicle, which is normally driven by the engine, is coasting down a hill. During that mode the accelerator is also released but the engine remains coupled to the drivetrain and the engine is kept running by the drive fuse of the gearbox main shaft.
The above mentioned heat recovery assembly is usually adapted to use waste heat of an internal combustion engine for other purposes, such as producing electric energy. From the state of the art a plurality of heat recovery assemblies are known. One of them is based on a Rankin cycle, which uses heat of an exhaust gas of the internal com-bustion engine for heating a working fluid which in turn drives an expander engine for generating electric energy.
The working fluid of a heat recovery assembly based on a Rankin cycle usually cycles through four stages, wherein in a first stage a liquid working fluid is pumped from low to high pressure. In the subsequent stage, the high pressure liquid working fluid enters a heating device, where it is heated by an external heat source, preferably a waste heat source of an internal combustion engine system, to be converted into its gaseous phase. In the next stage, the gaseous phase working fluid expands through an expander engine, for example a displacement expander, such as a piston engine, and/or a turbine, which is driven by the thermal energy of the working fluid. In its last stage, the working fluid is cooled down in a condenser and converted back to its liquid phase.
Disadvantageously, in conventional heat recovery assemblies the energy generation and the energy distribution generated of the heat recovery assembly cannot be controlled. Additionally, conventional heat recovery assemblies produce either electric energy or mechanical energy. For an expander engine producing electric energy this means e.g. that during high load ICE operation modes electric energy is generated in excess, wherein during low load ICE operation modes not enough electric energy is generated. If the heat recovery assembly acts as auxiliary power unit, the provision of additional propulsion energy may even be unwanted in low load ICE operation modes, particularly when the vehicle is running downhill.
It has therefore been suggested in the state of the art, e.g. EP 1 243 758 A1, to provide both a displacement expander for providing mechanical energy and an electric motor for generating electrical energy, which are connected by a Continuously Variable Transmission (CVT) for distributing and controlling the amount of energy produced by the displacement expander and by the electric motor.
However, even the transmission (CVT) disclosed in EP 1 243 758 A1 does not sufficiently solve the problem, as the CVT is expensive, interference-prone and needs a sophisticated control. Additionally, the CVT has a low efficiency due to energy losses at the transmission, which reduces the overall efficiency of the waste heat recovery system to such an extent that the energy surplus of the heat recovery system is negligible.
A further known problem of the conventional heat recovery assemblies occurs during low load ICE operation modes. During low load ICE operation modes, the temperature of the exhaust gas of the internal combustion engine decreases significantly, as the internal combustion engine more or less pumps fresh air at ambient temperature into the ex-haust gas system. A heat exchanger arranged at the exhaust gas system for operating the heat recovery assembly decreases the exhaust gas temperature even further. This results in at least two disadvantages:
i. The temperature of the exhaust gas is not sufficient for vaporizing the working fluid, thereby rendering the heat recovery assembly inoperable.
ii. An optionally arranged exhaust gas aftertreatment system, which usually requires a working temperature between roughly 250° C. and 450° C., is cooled below its working temperature.
Consequently, after a long period of low load ICE operation mode, e.g. after a downhill course, neither the heat recovery assembly nor the exhaust gas aftertreatment system are working properly.
It is desirable to provide an internal combustion engine system with a heat recovery system providing an improved energy distribution, wherein the heat recovery assembly is operable during all ICE operation modes.
According to a first aspect of the disclosure an internal combustion engine system with heat recovery is disclosed which comprises an internal combustion engine with a waste heat passage, an electric motor, a heat recovery assembly comprising a working fluid circulation circuit with a working fluid, a first heat source which is adapted to be heated by the waste heat passage and adapted to heat the working fluid, and an expander engine, which is operated by the heated working fluid, and a splitting device, which is connected to the electric motor and is adapted to be connected to a drivetrain of a vehicle and which splitting device is further connected to the expander engine, so that the expander engine is enabled to drive the drivetrain and/or the electric motor. The first heat source may e.g. be waste heat of the internal combustion engine through the waste heat passage. The splitting device may e.g. be a clutch or a power split. In case the expander engine is connected to the drivetrain of the vehicle, the expander engine is enabled to support the internal combustion engine in propelling the vehicle. In case the expander engine is connected to the electric motor, the expander engine is enabled to produce electric energy for driving an electric consumer.
The present disclosure is based on the idea to provide at least a second heat source for providing heat to the heat recovery assembly. Such a second heat source may be used for operating the heat recovery assembly, for example when the heat of the exhaust gas system of the internal combustion engine cannot provide enough heat or when the internal combustion engine is stopped, consequently producing no heat at all. Insufficient amounts of heat may also be produced during low load ICE operation modes, particularly during idle or motoring ICE operation modes.
During the above described low load ICE operation modes, the internal combustion engine is in principle pumping fresh air to the exhaust gas system whereby the temperature of the exhaust gas drops. Consequently, not enough heat is provided for vaporizing the working fluid and therefore operating the expander engine. A further disadvantage during such operating modes is that the exhaust gas aftertreatment system is air cooled in an uncontrolled and unwanted manner. In such cases, the second heat source may be activated for producing heat for operating the expander engine and for keeping the exhaust gas aftertreatment system within its working temperature range.
According to an embodiment the heat recovery assembly is adapted to be operable independently from operation of the internal combustion engine.
With this feature it is possible to operate the heat recovery assembly at another rate (or speed) than what would have been the case if it was operated together with the internal combustion engine. The heat recovery assembly may be operated at a higher or at a lower rate than the internal combustion engine. Hence it is enabled to operate the heat recovery assembly independently from the internal combustion engine.
According to an embodiment the second heat source is adapted to be operable independently from operation of the internal combustion engine.
With this feature it is possible to operate the second heat source at another rate (or speed) than what would have been the case if it was operated together with the internal combustion engine. The second heat source may be operated at a higher or at a lower rate (or speed) than the internal combustion engine. Hence it is enabled to operate the second heat source independently from the internal combustion engine. In particular this is advantageous when more energy is needed from the internal combustion engine system than what the internal combustion engine is able to deliver. In such a case the second heat source may provide heat to the heat recovery assembly, which in turn delivers energy to the splitting device where it may be further delivered to an energy consumer.
According to an embodiment the heat recovery assembly and/or the second heat source is adapted to be operable when the internal combustion engine is shut off.
In particular this feature is advantageous when the internal combustion engine has been shut off such that it cannot deliver any energy at all. The heat recovery assembly and/or the second heat source may instead be the source of energy production and delivery through the splitting device to an energy consumer. Generally, providing a second heat source has the advantage that in case the demand for the combustion engine is low, it is possible to stop the internal combustion engine completely, and to drive the vehicle with help of the expander engine, only. Additionally, when the vehicle is at standstill and used as a sleeper, electric energy can be provided by the heat recovery assembly, which is operated by the second heat source. Advantageously, the heat recovery assembly may also drive the drivetrain of the vehicle, which in turn enables a driver to drive the vehicle without starting the internal combustion engine. This is particularly preferred for moving trucks or motorhomes at a parking lot or on a camp site.
As mentioned above, the second heat source may heat the working fluid of the heat recovery assembly or the exhaust gas system. In the latter case, beating the exhaust gas system may be performed by producing hot exhaust gas or by heating the exhaust gas of the internal combustion engine. Heating the exhaust gas system has the advantage that the exhaust gas aftertreatment system may be kept within its working temperature range even during a standstill period or during low load ICE operation modes so that a cold start of the exhaust gas aftertreatment may be avoided. According to an embodiment the second heat source is a heater for heating the working fluid of the heat recovery assembly.
According to an embodiment the waste heat passage is an exhaust gas system comprise at least an exhaust gas aftertreatment system for guiding at least part of an exhaust gas from the internal combustion engine to an environment.
According to an embodiment, the second heat source is a heater for heating the exhaust gas in the exhaust gas system. It is further possible to provide even more than one additional heat source, particularly a second heat source as heater for heating the exhaust gas and a third heat source for heating the working fluid. The one and the same second heat source may also be arranged to heat one or several of these items in combination.
According to an embodiment the second heat source is a burner for burning fuel, comprising a fuel inlet and an air inlet, and an exhaust gas outlet, which is connected to the exhaust gas system of the internal combustion engine for providing hot exhaust gases to the exhaust gas system. The hot exhaust gas of the burner may be used for operating the heat recovery assembly by exchanging heat at the heat exchangers and for keeping the exhaust gas aftertreatment system within its working temperature range.
According to an embodiment, the exhaust gas outlet of the burner is connected to the exhaust gas system (16) of the internal combustion engine upstream of the exhaust gas aftertreatment system
Instead of providing an extra burner, it is also possible to use an already existing preheating system for the exhaust gas aftertreatment system as second heat source.
According to an embodiment, the heat recovery assembly further comprises at least one heat exchanger, which is connected to a waste heat source of the internal combustion engine. Usually, the internal combustion engine has an exhaust gas outlet side, which is connected to an exhaust gas system comprising at least an exhaust gas duct, an optional turbine for driving a turbocharger and an optional exhaust gas aftertreatment system. The exhaust gas system may further comprise an exhaust gas recirculation system for recirculating exhaust gas to the internal combustion engine and a cooling device for cooling the recirculated exhaust gas. Waste heat of the internal combustion engine, which may be hot exhaust gas, streams through the exhaust gas system of the internal combustion engine, which may be used for operating the heat recovery assembly. For that at least one heat exchanger may be arranged at a suitable location in the exhaust gas system.
A different source of waste heat may be the cooling system of the internal combustion engine. Instead of using a radiator for cooling the internal combustion engine coolant, a heat exchanger may be used which is adapted to vaporize the working fluid of the heat recovery assembly by using the heat of the coolant. The coolant in turn is cooled down.
Advantageously in all cases, the thermal energy of the waste heat may be converted by the expander engine into electric or mechanical energy, which may be used for operating electric devices or as auxiliary power for the propulsion of the vehicle.
According to an embodiment, at least one heat exchanger is arranged at the ex-haust gas duct itself, downstream or upstream of an optional exhaust gas aftertreatment system and/or at an exhaust gas recirculation duct (EGR duct). Arranging the heat exchanger downstream of the exhaust gas aftertreatment system has the advantage that the hot exhaust gas leaving the exhaust gas aftertreatment system may be used. Since the exhaust gas aftertreatment system is operating in a working temperature range between ca. 250° C. and 450° C., also the exhaust gas leaving the exhaust gas aftertreatment system has a comparable temperature range. This temperature may even be higher than the temperature of the exhaust gas upstream of the exhaust gas aftertreatment system. For instance, this may be the case if a turbine is used for driving a turbocharger, which is arranged upstream of the exhaust gas aftertreatment system. Arranging the heat exchanger upstream of the exhaust gas aftertreatment system amplifies the cooling of the exhaust gas upstream of the exhaust gas aftertreatment system. Cooling the exhaust gas upstream of the exhaust gas aftertreatment system in turn may cause a significant temperature drop in the exhaust gas aftertreatment system, which compromises its efficiency.
According to an embodiment, a first heat exchanger is arranged downstream of the exhaust gas aftertreatment system and a second heat exchanger is arranged upstream of the exhaust gas aftertreatment system. The advantage of such an arrangement is twofold:
i. If the temperature of the exhaust gas upstream of the exhaust gas after-treatment is very high, particularly exceeding the working temperature of the exhaust gas aftertreatment system, the working fluid can be superheated by the second heat exchanger, which increases the energy exploit of the expander engine.
Simultaneously, the temperature of the exhaust gas is lowered into the working temperature range of the exhaust gas aftertreatment system, whereby the life time of the exhaust gas aftertreatment system is prolonged.
ii. If the temperature of the exhaust gas is low, particularly below the working temperature range of the exhaust gas aftertreatment system, the second heat exchanger heats the exhaust gas, whereby the exhaust gas aftertreatment system may be kept within its working temperature range.
In the preferred case, where two heat exchangers are arranged upstream and downstream of the exhaust gas aftertreatment system, the additional heat source is preferably arranged between the two heat exchangers. Thereby, the hot working fluid may also heat the exhaust gas upstream of the exhaust gas aftertreatment system. The hot exhaust gas upstream of the exhaust gas aftertreatment system in turn keeps the exhaust gas aftertreatment in its working temperature range. The heat exchanger downstream of the exhaust gas aftertreatment system in turn returns part of the heat to the working fluid circuit.
According to an embodiment, at least one of the heat exchangers may be arranged at an exhaust gas recirculation duct of an internal combustion engine with exhaust gas recirculation (EGR engine). In an EGR engine, the emissions of the internal combustion engine are reduced by recirculating part of the total exhaust gas flow. The recirculated sub-flow of exhaust gas is cooled before fed into the gas intake side of the EGR engine, where it is mixed with incoming air before the mixture is introduced into the cylinders of the EGR engine. Cooling of the recirculated exhaust gas is preferable for the EGR engines as recirculating hot exhaust gas would increase the temperature of the gas at the gas intake side of the EGR engine to a level, which otherwise could damage the EGR engine. Moreover, recirculation of exhaust gas amounts in the range of 15-30% of the total mass flow through the EGR engine is desirable for yielding a sufficient NOx reduction. Thereby, the cooler of the EGR engine may be used for simultaneously heating the working fluid and cooling the recirculated exhaust gas. Preferably, also in the EGR system with heat recovery, a second heat exchanger arranged upstream of the exhaust gas after-treatment system may be used, providing the above discussed advantages.
According to an embodiment the splitting device may be at least one clutch or a clutch arrangement, which is operated to connect and disconnect the drivetrain and/or the electric motor. Additionally or alternatively, an epicyclic or planetary gear power split device may be used.
Regardless what kind of splitting device is used, the advantage of the simple splitting device is that it only connects or disconnects the expander engine to the drivetrain and to the electric motor and does not distribute the power of the expander to the drivetrain and the electric motor as known from the state of the art.
Further, the splitting device may be adapted to provide a connection between the drivetrain and the electric motor.
According to an embodiment, the electric motor may be connected to an electric energy storing device such as a battery or a capacitor. With this arrangement, it is even possible to decouple the heat recovery assembly, namely the expander engine, completely and drive the drivetrain by means of the electric motor, only.
Alternatively or additionally, the splitting device may be operated in such a way that the drivetrain is connected to the electric motor. Thereby, the electric motor may be used as electric motor, which may drive the drivetrain of the vehicle. Further, a power storing device, such as a battery, may be present, which is adapted to drive the electric motor. On the other hand, when the electric motor is driven by the expander engine or by the drivetrain, electric energy may be produced by the electric motor and stored in the power storing device.
According to an embodiment the second heat source is adapted to run on the same fuel as the internal combustion engine, which simplifies the design internal combus-tion engine system.
According to an embodiment the expander engine is adapted to operate the electric motor as generator for providing electric energy to a vehicle.
According to a second aspect a vehicle is disclosed which comprises an internal combustion engine system of the above disclosed kind.
According to an embodiment the vehicle comprises further auxiliary equipment, such as a heating system for a passenger cab, wherein the electric motor is operably connected to the auxiliary equipment for operation thereof.
Further advantages and preferred embodiments are described in the attached claims, the specification and the drawings.